I have been using just my coaster brake for five years and had no problems. Yes, it does not stop very quickly but, I have always been able to stop in time.
Just recently I added caliper brakes to my front, getting ready for some serious down hill mountain riding. It was very simple to add and only took a few minutes.
The only thing I had to do was pinch my front fender a bit to give the clearance that I needed.
If you want to stop better...you really have no option other then to add a front brake.
